Anal sphincter muscles

Anal Sphincter Muscles

Diagram of the anal canal, with the sphincter muscles labeled at right.

The anal sphincter muscles are a group of muscles that surround the anus, controlling the release of feces from the body. These muscles are part of the pelvic floor and are essential for maintaining continence.

Anatomy

The anal sphincter complex consists of two main muscles: the internal anal sphincter and the external anal sphincter.

The internal anal sphincter is a thick, smooth muscle layer that is involuntary and maintains constant contraction. It is supplied by the autonomic nervous system.

The external anal sphincter is a layer of voluntary muscle that surrounds the internal sphincter. It is controlled by the pudendal nerve and can be consciously relaxed and contracted.

Function

The primary function of the anal sphincter muscles is to control the expulsion of feces from the body. The internal sphincter maintains constant tension to prevent leakage, while the external sphincter provides conscious control over the release of feces.

Clinical significance

Damage or dysfunction of the anal sphincter muscles can lead to conditions such as fecal incontinence or anal fissure. Treatment options include sphincteroplasty, sacral nerve stimulation, and biofeedback therapy.

See also

• Pelvic floor
• Defecation
• Gastrointestinal tract